acta_architectura.sggw.pl
O R I G I N A L P A P E R Received: 09.05.2019
Accepted: 14.07.2019
INTRODUCTION
For many years, the effective techniques of strength- ening both soil in road construction and roadway pa- vement were sought. Most often these techniques of strengthening is performed in order to increase the re- sistance of roadway, to reduce the effects of appeared settlement and another external influence. In order to meet a number of functions that significantly contri- bute to the improvement of roadway performance and subgrade quality, geosynthetics are successfully used (Gradkowski, 2007; Kazimierowicz-Frankowska, 2013; Szczygielski & Stopa, 2014; Keller, 2016).
THE CLASSIFICATION OF THE GEOSYNTHETICS Currently, the availability of geosynthetics is very high. In accordance with the PN-EN ISO 10318-
-1:2015 standard on geosynthetic (GSY) it is possible to define it as a generic term describing a product, at last one of whose components is made from a syn- thetic or natural polymer, in the form of a sheet, a strip or a three – dimensional structure, used in contact with soil and/or other materials on geotechnical and civil engineering applications. The geosynthetics can gen- erally be categorized based on the production method.
In the technical literature the following categories are recognized: geotextiles, geogrids, geonets, geomem- branes, geosynthetic clay liners, geopipes, geofoams and geocomposites (Horodecki & Duszyńska, 2017).
However, according to the PN-EN ISO 10318-1:2015 standard on geosynthetics (GSY) it is possible to di- vide them into the following groups:
− geotextile (GTX), which include: no-woven geo- textile (GTX-NW), knitted geotextile (GTX-K), woven geotextile (GTX-W);
THE FUNCTIONS OF THE GEOSYNTHETICS IN ROADWAY APPLICATIONS
Kinga Brózda
, Jacek Selejdak
Faculty of Civil Engineering, Częstochowa University of Technology, Częstochowa
ABSTRACT
The aim of the study was to analyse the possibilities of using geosynthetics in communication engineering, especially road construction. The availability of geosynthetic products was described. These geosynthetics were classified and described in general due to the production method. Particular attention to the functions, which the geosynthetics can fulfill in roadway applications was paid. In details the possible location of geosynthetics in individual roadway layers was shown and then the performed functions were presented. It was also pointed out which of these functions the particular types of geosynthetics perform. In addition, the possibility of using the geogrids made of glass fibers and the geocomposites consisting of the fiberglass geogrid combined with a no-woven polypropylene were discussed. The benefits of using this type of geosynthetics were mentioned.
Key words: classification, location of geosynthetics, function, fiberglass geosynthetics
− geotextile-related product (GTP), which include:
geogrid (GGR), geonet (GNT), geomat (GMA), geocell (GCE), geostrip (GST), geospacer (GSP);
− geosynthetic barrier (GBR), which include: poly- meric geosynthetic barier (GBR-P), clay geosyn- thetic barier (GBR-C), bituminous geosynthetic barier (GBR-B);
− geocomposite (GCO).
These types of the geosynthetics are described and characterized in Table 1 (Bathurst, 2007; Koerner, Hsuan & Koerner, 2007; Palmeira, Tatsuoka, Bathurst, Stevenson & Zornberg, 2008; Duszyńska & Sikora, 2014).
Such a wide assortment of geosynthetic products enables proper selection of design parameters to en- sure optimal quality and roadway performance.
FUNCTIONS OF THE GEOSYNTHETICS IN ROADWAY APPLICATIONS
The particular types of the geosynthetics are design to fulfill specific functions. The main functions of the geosynthetics, which are reported in the technical li- terature (Koerner et al., 2007; Palmeira et al., 2008;
Szruba, 2014; PN-EN ISO 10318-1:2015), include:
− separation – means a separation of the subsoil from the structural layer, or separation of indivi- dual structural layers from aggregates with dissi- milar parameters. Placed between two different material, the geosynthetic keeps the functionality and integrity of these two materials and sometimes provides a long-term stress relief. The main design properties to fulfill this function concern its sur- vivability during installation;
Table 1. The classification of the geosynthetics and descriptions Type of
geosynthetics Description Scheme
Geotextiles
Mainly take the form of continuous sheets which are woven, non-woven, knitted or stitch-bonded by fibers or yarns. These sheets are permeable as well as flexible, and generally have the appearance of a fabric
Geogrids
A spatial geosynthetics with cellular structure, most often made of HDPE (high density polyethylene) in the form of geogrids (strips connected by welding at points) or rigid modular panels connected with locks
Geonets
A type of flat geosynthetics, with a perpendicular arrangement of bands forming meshes, usually made of PP (polypropylene), PE (polyetylene), polyester, fiberglass or PVAL (polyvinyl alcohol). Appear in the form of interlaced fibers (with flexible nodes), welded fibers (with rigid nodes), or have a homogeneous grate structure Geomembranes A continuous and flexible sheets which are manufactured from one or more
synthetic materials
Geocomposites
Made of combination of two or more types of geosynthetics, for example:
geotextile-geonet, geonet-geomembrane, geotextile-geogrid or geosynthetic clay liner etc.
Geosynthetic clay liners
Prefabricated geosynthetics with a bentonite clay layer, which usually is placed between a top and bottom geotextile layer. Sometimes geotextile bentonite which is bonded to a geomembrane or single layer of geotextile, is stitched or needle punched to increase internal shear resistance
Geopipes Perforated or solid-wall polymeric pipes, which in some case are wrapped with a geotextile filter
Geofoams In the form of blocks or plates are formed by the expansion of the PS (polystyrene) foam to form a network of closed gas-filled cells, which density is low
− filtration – a free liquid flow between soil layers, while maintaining the intact structure of the soil phase. The geosynthetic retains fine particles on its upstream. The main design properties to fulfill this function are a permittivity (cross-plane hydraulic conductivity per unit thickness) and measures its pore-size distribution;
− drainage – an ability to drain liquids (or gasses) within the plane of the geosynthetic’s structure.
The main design property to fulfill this function is a transmissivity which is an in-plane hydraulic conductivity in relation to the thickness;
− reinforcement – includes the reinforcement of the soil (to improve the mechanical properties of soil, structural layers, as well as slope stability condi- tions) and reinforcement of the roadway pavements (to reinforce the bituminous masses with geosyn- thetics, also to enhance the surface of dirt roads).
The main design property to fulfill this function is a tensile strength of geosynthetic;
− surface erosion control – use of a geosynthetic ma- terials to prevent or limit soil or other particle move- ments at the surface of, for example, a slope. Produ- ces a tensile forces which control the deformations in the soil-geosynthetic composite (Zornberg, 2017).
The main design property to fulfill this function is the stiffness of the soil-geosynthetic composite;
− protection – means a protection against mechanical damage of other geosynthetics, against falling rock fragments and also as an additional fixation of other geosynthetics. The geosynthetic creates a cushion above or below other material with the purpose of minimize damage during placement of other over- lying materials. The main design properties to fulfill this function concern its puncture resistance;
− barrier – minimizes the cross-plane flow of liquids or gasses and provides containment of it. The main design property to fulfill this function concerns a long-term durability of the geosynthetic;
− stress relief – (for asphalt overlay) use of a geosyn- thetic to retard the development of cracks by absor- bing the stresses arise from the damaged pavement.
These listed functions are used, among others, to im- prove the utility parameters of the roadway. Therefore, in roadway applications the geosynthetics are used in order to limit the reflective cracking in asphalt overlays,
to stabilize the road base and road subgrade, to provide separation and lateral drainage (Zornberg, 2017).
The possible geosynthetic locations in the paved road section were presented in the figure (Gradkow- ski, 2007; Zornberg, 2017). Various functions that these geosynthetics can meet in selected locations were also submitted.
Fig. Selected functions of geosynthetics fulfilled de- pending on various location in roadway layer (ba- sed on Gradkowski, 2007; Zornberg, 2017)
Table 2. Functions of the geosynthetics depending on their types
Type
of geosynthetic
Function
separation filtration drainage reinforcement protection barrier
Geotextiles + + + + +
Geogrids +
Geonets +
Geomembranes + + +
Geosynthetic clay liners +
Geopipes +
Geofoams +
Geocomposites + + + + + +
The various types of the geosynthetics are suc- cessfully used to fulfill one or more specific functions in a variety of roadway applications (Szruba, 2014;
Zornberg, 2017). Table 2 shows which types of geo- synthetics meet selected functions.
THE FIBERGLASS GEOSYNTHETICS IN ROADWAY APPLICATIONS
The resistance of the asphalt overlays to the formation of the cracks and their propagation can be considered as one of the most important mechanical property (Grabowski & Pożarycki, 2006). The reinforcement of roadway made of geosynthetics can in a significant way delay this propagation process of asphalt pave- ment cracks. Undeniably important issue is checking the effectiveness and efficiency of using these ma- terials as the reinforcement of asphalt surfaces. One of the increasingly common solutions is the use of glass fiber reinforced geosynthetics. The fiberglass reinforced plastics (FRP) geogrid has a broad scope of use because of high strength and stability, very good resistance to environmental factors and also creep, which are achieved by the appropriate choice of the raw material, production process and quality index (Brózda, Selejdak & Koteš, 2017). Efficacy of this type of solution were demonstrated by Zhesheng, Hao, Qingshan and Chunlong (2015). It was proved, among others, that it is possible to strength the inter- face bonding by using glass fiber reinforced asphalt membranes and there is potential to limit the reflection cracking of asphalt concrete (AC) overlay on Portland cement concrete (PCC) pavements.
The most common is the use of glass fiber geogrids or geocomposites consisting of a fiberglass geogrid combined with a no-woven polypropylene. Then the meshes of such a geogrid are created by longitudinal and transverse arrangement of the fibers (warp and weft). The warp and weft are interlaced in the nodes so that the warp can be moved along the weft, which allows the course of the fibers to match the grains of the asphalt layer. In some cases, this type of mesh is also soaked with asphalt to merge glass fibers, to pro- tect the fibers from mechanical damage as well against the effects of chemical substances, and improving ad-
hesion to asphalt layers (Mujah, Ahmad, Hazarika &
Safari, 2013; Qingbiao et al., 2015).
Geosynthetics made of glass fiber reinforced pla- stics are widely used in the field of strengthening due to the high strength parameters, good ductility and re- sistance to environmental factors, resistance to creep and high stability (Brózda et al., 2017). The benefits of using this type of geosynthetics can also include the reduction of ruts resulting from high ambient tempe- ratures, intensive loads from vehicle wheels, and also extended fatigue life of pavements.
SUMMARY
The improvement of the roadway performance and quality of the subgrade is possible by using various types of the geosynthetics. These geosynthetics are able to meet a number of specific functions, often more than one. On the base of the theoretical studies and practical applications the extension of service life of flexible pavements by installing geosynthetics was proved. Moreover, some of the geosynthetics (for example geogrid) can be applied in the new con- structions and also rehabilitation of existing asphalt pavements.
Especially in the roadway applications, the geo- grids placed at the interface of bituminous layers improve the rutting resistance and prevent or totally eliminate the reflective cracking. In addition, depen- ding on the geosynthetic’s location in the paved road section, it is possible to achieve the required effect on the structure of the roadway. However, it is important to pay attention on the design property of the geosyn- thetic products. It is necessary to fulfill the specific functions.
Recently, there is also a growing interest in modern materials for the geosynthetic’s production, such as FRP with glass fibers, especially as the reinforcement of asphalt overlays. The reason is, among others, very good properties of the raw material. Nevertheless, in order to improve the techniques of strengthening the roadway surfaces as well as the ground soil in road construction, the theoretical studies and practical ap- plications are still recommended.
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ZASTOSOWANIE GEOSYNTETYKÓW W BUDOWNICTWIE DROGOWYM
STRESZCZENIE
Podstawowym celem pracy była analiza możliwości wykorzystania geosyntetyków w inżynierii komunika- cyjnej, a w szczególności w budownictwie drogowym. Opisano rodzaje dostępnych produktów geosyntety- cznych. Zaprezentowano klasyfikację geosyntetyków ze względu na metodę produkcji oraz krótko scharak- teryzowano dostępne na rynku wyroby geosyntetyczne. Szczególną uwagę zwrócono na funkcje i zastoso- wanie, jakie geosyntetyki mogą spełniać w podłożach nawierzchni drogowych. Dokładnie opisano miejsce wbudowania geosyntetyków w poszczególnych warstwach drogowych oraz pełnione przez nie funkcje oraz wskazano, które z nich realizowane są przez poszczególne rodzaje geosyntetyków. Ponadto omówiono możliwość wykorzystania geosiatek wykonanych z włókien szklanych i geokompozytów składających się z siatki z włókna szklanego połączonej z geowłókniną polipropylenową. Wskazano również zalety zastoso- wania tego typu geosyntetyków.
